Transformer secondary

[bwyllie]

Re: Transformer secondary

Lady Sparks Lover,

My company follows the same design standards and the reason I wrote the question is in a design review I notice another engineer firm with different ampacities but from this forum I figured that they use the 90 degree column, for all of our sizing we use the 75 degree column.

 

[dereckbc]

Re: Transformer secondary

Originally posted by lady sparks lover:

You know Dereck, I haven't measured a technology panel over that, but all I can say is in the work that I do (mainly schools with technology panels with serve only computers), there is always at least 100%. I would think that would be enough to warrant:


1. you'll have 4 CCC in one conduit.

2. distorted voltage wave patterns.

If none else, the 80% derating is applicable.

It was my thought that the K-rated Xfmr is just insulated at the cores to prevent over heating, but does little to correct the distorted waves forms caused by harmonics.

I could be wrong you know...

I agree. To my knowledge ther is nothing that will prevent harmonic on the electrical system. You can use devices like zig-zags, filters, etc to trap the harmonics and absorb the heat, but it is still there none the less. The answer lies in the switch mode rectifiers using power factor correcting circuitry, which is comming onto the market due to demand. You are right, a "K" rated transformer only handles the heat, not correct the problem.

Where I used to work required 150% neutral oversizing, but after tons of data I collected over the years, I began to question the practice, as I rarely could ever even find it aproaching 100%. Just fishing to see if anyone has any documented cases where neutral current exceeds 100% because the Telco I work for now has no standard, and they do not like the message I am giving them to at least go 100 % with 13 K rated transformers.